This invention relates to control of the feed of multi-strike ink ribbons and in particular to the control of insertion of cassettes containing such ribbons into printing apparatus.
Multi-strike ink ribbons are ribbons in which a part of the ink is removed in a pass of the ribbon past a print head so that the ribbon may be re-used a number of times in which the ink is successively removed. In thermal ink transfer ribbons the ink is in multiple layers carried on a backing substrate and in each pass of the ribbon ink from the exposed layer is removed leaving ink in underlying layers to be removed in successive passes of the ribbon. In printing devices in which printing is carried out during feeding of an item, on which printing is to be effected, past a print head in a single direction it has been required that, when the end of the ribbon is reached after a pass of the ribbon, printing is interrupted to enable the entire ribbon to be rewound. In a multi-strike ink ribbon feed disclosed in our European patent specification 0 315 384 the disadvantage of interrupting the printing for a time sufficient to enable the ribbon to be rewound is overcome by progressively rewinding the ribbon in intervals between printing on items. However whether the entire ribbon is rewound in a single operation or is progressively rewound it is necessary to provide drive means to rotate the spool on which the ribbon is wound. Such drive means add to the cost of the equipment and furthermore occupy space so that the equipment be larger than desired.
Ink ribbons may be provided in a cassette which may be removably inserted in operative position in a printing device. The cassette usually has a supply spool filled with ribbon and an empty take-up spool onto which the used ribbon is wound, When the cassette is in operative position in the printing device, means in the printing device draws the ribbon from the supply spool past the print head of the printing device and take up spool is driven by a drive motor in the printing device to wind the used ribbon onto the take-up spool.